One-Step Synthesis of Ultrathin High-Entropy Layered Double Hydroxides for Ampere-Level Water Oxidation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript reports on the one-step synthesis of ultrathin, high-entropy layered double hydroxides for use as a catalytic platform for water oxidation. The material exhibits exceptional electrochemical activity and stability, demonstrating low overpotential and fast kinetics, making it a potentially useful tool in electrochemical measurements. Before publication, there are some comment to be considered:

1. It is best to show the polarization curves of nickel foam only as working electrode in order to determine the background current, for which Ni2+ + 2e−  ⇌  Ni(s) and Ni(OH)2 + 2e−  ⇌ Ni(s) + 2OH− reactions should not take place. 

2. Figure 1a suppose to show which color represent which element.

 

Overall Merit:

The  manuscript certainly has some merit and I believe that the  is organized in a logical and understandable manner.

Author Response

Reply to Reviewer 1

This manuscript reports on the one-step synthesis of ultrathin, high-entropy layered double hydroxides for use as a catalytic platform for water oxidation. The material exhibits exceptional electrochemical activity and stability, demonstrating low overpotential and fast kinetics, making it a potentially useful tool in electrochemical measurements. Before publication, there are some comment to be considered:

Response: Thank you very much for your hard work on reviewing our manuscript. Your comments are highly insightful and enable us to greatly improve the manuscript. We have revised the manuscript carefully according to your suggestions. Details of the corresponding revisions are described below point by point.

1. It is best to show the polarization curves of nickel foam only as working electrode in order to determine the background current, for which Ni²⁺ + 2e⁻ ⇌  Ni(s) and Ni(OH)₂ + 2e⁻  ⇌ Ni(s) + 2OH⁻ reactions should not take place.

Response: Thank you very much for your valuable comment. The polarization curve of bare nickel foam is depicted in Figure S5a, with its associated redox peaks illustrated in Figure S5b. The redox peaks corresponding to Ni²⁺/Ni³⁺ were detected between 1.1-1.6 V vs RHE. Notably, no redox peaks for Ni⁰/Ni²⁺ were observed within the tested voltage range due to their occurrence typically around -0.257 V vs RHE, thereby not contributing to background current.

Revisions made in the Manuscript:

“Additionally, the polarization curve of bare nickel foam is depicted in Figure S5a, with its associated redox peaks illustrated in Figure S5b to determine the background current. The redox peaks corresponding to Ni²⁺/Ni³⁺ were detected between 1.1-1.6 V vs RHE. Notably, no redox peaks for Ni⁰/Ni²⁺ were observed within the tested voltage range due to their occurrence typically around -0.257 V vs RHE.”

Figure S5. (a) Ploarization curves of NiFe-LDH, NiFeZnCoCr-LDH, U- NiFeZnCoCr-LDH and Ni foam. (b) The redox peaks of Ni foam.

2. Figure 1a suppose to show which color represent which element.

Response: Thank you for pointing this out. The labels of elements have been supplied in Figure 1a.

Revisions made in the Manuscript:

Figure 1. (a) Synthetic scheme of U-NiFeZnCoCr-LDH.

Reviewer 2 Report

Comments and Suggestions for Authors

The author developed a simple method for synthesizing high entropy layered double hydroxides with an ultra-thin structure. This material not only exhibits excellent oxygen evolution reaction (OER) performance, but also maintains a low potential decay rate at high current density for an extended period.

The manuscript is recommended for publication in Catalysts after minor revisions. My detailed comments are as follows:

1. In Figure 1e, the EDS-mapping images indicate a large amount of Zn in this material, which contradicts the feed ratio used in the synthesis. Please provide an explanation.

2. From Fig.2a, it can be observed that the peak at 1360cm^-1 remains present in the spectrum of U-LDH, potentially indicating the existence of carbonates in the interlayer. Consequently, does this imply a failure in the stripping strategy?

 

3. Based on Figures 4a and 4b, it appears that high-entropy LDH exhibits excellent stability. It is important to quantify the ratio of various metal elements after the stability test.

Author Response

Reply to Reviewer 2

The author developed a simple method for synthesizing high entropy layered double hydroxides with an ultra-thin structure. This material not only exhibits excellent oxygen evolution reaction (OER) performance, but also maintains a low potential decay rate at high current density for an extended period.

The manuscript is recommended for publication in Catalysts after minor revisions. My detailed comments are as follows:

Response: We are grateful for the time and effort the reviewer had spent on our manuscript, and deeply appreciate the valuable review and positive comments of our manuscript, which have helped improve the manuscript quality.

1. In Figure 1e, the EDS-mapping images indicate a large amount of Zn in this material, which contradicts the feed ratio used in the synthesis. Please provide an explanation.

Response: The quantitative analysis results of EDS in Figure 1e reveal that Zn comprises 28.2% of the atomic ratio, which is only slightly higher than other M²⁺ elements (Ni at 22.2% and Co at 22.3%). Conversely, the results in Figure 1f seem to suggest a higher Zn content. This discrepancy arises from the fact that EDS-Mapping signal intensity is influenced by the mass ratio of elements rather than the atomic ratio as depicted in Figure 1e. Furthermore, Zn, with a higher relative atomic mass (65.41) compared to Ni (58.69) and Co (58.93), contributes to this observation.

Element	Ni	Fe	Zn	Co	Cr
Mass ratio (%)	21.95	13.18	31.07	22.14	11.65

Appendix Table 1. Mass ratio of each elements in U-NiFeZnCoCr-LDH.

2. From Fig.2a, it can be observed that the peak at 1360cm^-1 remains present in the spectrum of U-LDH, potentially indicating the existence of carbonates in the interlayer. Consequently, does this imply a failure in the stripping strategy?

Response: Thank you very much for your valuable comment. The similar vibration frequencies and modes of nitrate and carbonate pose challenges in their differentiation using FTIR spectroscopy. As noted in the manuscript, "U-NiFeZnCoCr-LDH exhibits a prominent C=O stretching vibration peak at 1692 cm^-1, associated with the amide group of FA," indicating robust adsorption between FA and U-LDH. The successful exfoliation of the material is further supported by the combined findings of Figure 1b and Figure 1d.

3. Based on Figures 4a and 4b, it appears that high-entropy LDH exhibits excellent stability. It is important to quantify the ratio of various metal elements after the stability test.

Response: Thank you very much. Following the chronopotentiometric test, the electrolyte underwent ICP-MS analysis to quantitatively determine the ratios of dissolved metal ions in U-NiFeZnCoCr, as detailed in Appendix Table 2. The results indicate similar dissolution levels across various metal elements, contributing to the stability of U-NiFeZnCoCr-LDH.

Element	Ni	Fe	Zn	Co	Cr
Mass (ppm)	16.56	16.14	18.11	15.54	17.06

Appendix Table 2. ICP-MS results of the electrolyte after chronopotentiometric test.